A hetero-structure field effect transistor is known from International patent application publication WO 2005/079370. The hetero-structure field effect transistor includes an AlGaN/GaN interface that obtains a high current carrying channel. The bidirectional switch operates with at least one gate that prevents or permits the establishment of a two dimensional electron gas to form the current carrying channel for the bidirectional switch.
From International patent application publication WO 2006/052052 a semiconductor device is known. The semiconductor device has a base plate made from n-doped GaN (n-GaN) with a low resistance. A drain electrode is formed on the base plate. A top surface of the semiconductor base plate is covered by an insulating layer formed from AlN, leaving a non-covered surface. A top surface of the insulating layer is covered by a semiconductor layer with a lower semiconductor layer made from n-GaN and an upper semiconductor layer made from AlGaN. A gate electrode made from polysilicon is formed, via a gate insulating layer, on a top surface of the upper semiconductor layer. A source electrode made from aluminium makes ohmic contact with the surface of the upper semiconductor layer. However, a disadvantage of the semiconductor device disclosed in this publication is that the semiconductor device exhibits a large leakage current since, although it is described that a 2 dimensional electron gas (2DEG) is obtained, the flowing electrons are not confined to a 2-dimensional region but can actually flow from source to drain over the whole thickness of the lower semiconductor layer, even when a negative voltage is applied at the gate electrode.
Ben-Yaacov et al, “AlGaN/GaN current aperture vertical electron transistors”, Device research conference, 2002. 60th DRC Conference digest Jun. 24-26, 2002, Piscataway, N.J. USA IEEE, p. 31-32, discloses an AlGaN/GaN current aperture vertical electron transistor (CAVET). The cavet consist of a source region separated from a drain region by an insulating layer. The insulating layer includes a narrow aperture which is filled with conducting material. A Schottky gate is located directly above the aperture and is used to modulate the current passing through the aperture.
However, a disadvantage of the device disclosed in this ‘Ben-Yaacov’ publication is that in operation it exhibits relatively high resistive losses and the high leakage current does not enable to operate the device in a off-state configuration up to a breakdown source-drain voltage.